1. Field of the Invention
The present invention generally relates to electrical waveform generators and, in particular, to such generators which produce an analog waveform output in response to sequences of digitally-represented values.
2. Statement of the Prior Art
Since the development of digital-to-analog converters, it has been possible to store electrical waveforms as digital information in the form of sequential amplitude values and to therefrom reproduce the electrical waveform so represented by sequentially coupling the digital amplitude values to a digital-to-analog converter. The various improvements that have been made in digital-to-analog converters have allowed and generally caused increased use of this technique for digitally storing and then reproducing an electrical waveform as an analog signal. The initial applications of this process were generally in the area of waveform display and measurement. However, as the circuitry for performing this technique underwent development, attempts were made at expanding the various applications due to the relatively great flexibility available in defining a waveform by its sequential amplitude values. Various improvements that have been made in the output circuitry are exemplified and explained by U.S. Pat. Nos. 3,621,228; 4,355,367; and 4,438,503. The waveform generators or synthesizers described by these patents operate directly in the sense of conditioning and converting digital information into a desired analog waveform. As is evident from the latter two of these patents, there has been increased emphasis on applying this general technique to various specific purposes such as the ones shown of generating audible and VOR waveforms.
Interest in expanding the capabilities of this technique continues for the purpose of providing a flexible waveform generator which is useful for many applications. However, one of the disadvantages of the existing generators which must be overcome in order to meet this need is the relative size and flexibility of the storage space used for holding data points. Although it is possible to repetitively loop through existing memories, greater flexibility is still required to meet the needs of automated test equipment and systems.